This invention relates to improvements in devices for intravascular ultrasound (IVUS) guided catheter systems.
Intravascular ultrasound is a rapidly evolving imaging technique most commonly employed in coronary and iliofemoral arteries. The technique has the potential to facilitate the study of aneurysm progression, atherosclerosis or dissection and to outline the effect of endovascular intervention in more detail than angiography.
The presently used intravascular ultrasound systems fall into two categories: stationary electronic systems and mechanically driven rotating transducer systems. In both systems, an acoustic element or transducer is used to transmit a signal, which impinges upon, and reflects from, surfaces of different acoustic densities, which the signal encounters. An acoustic transducer receives the reflected wave. These data are sent to a processing system via an electrical cable where they are manipulated and displayed as an image. The systems are mounted to catheters, or axially elongate structures, which are routed through body lumens such as arteries to reach the site of imaging.
The non-rotating or stationary catheter of the stationary electronic system houses an array of small acoustic elements, which are positioned cylindrically at the catheter tip. After positioning the catheter in a vessel, body lumen or cavity, subgroups of acoustic elements may together generate an echo image. The spacing between the acoustic elements in the transducer array creates areas where the acoustic signal is neither transmitted nor received. When the data is processed, gaps of missing information occur, resulting in a poor quality image. The advantage of the stationary electronic system is that the catheter is very flexible and a central lumen is available for guidewire insertion. No distortion of the image, due to inhomogeneous mechanical rotation, is present. The stationary catheters are reliable and inexpensive but produce a poor quality image.
The mechanical intravascular ultrasound-imaging catheter comprises a mechanically rotating catheter shaft with a single ultrasound transducer. Either the acoustic element rotates or the acoustic element is stationary and a mirror rotates. In this manner, the acoustic signal is transmitted and received in a continuous 360-degree sweep. There are no gaps in the data and a higher quality image results. Realizing a driving mechanism while keeping the catheter fully flexible and steerable as well as miniature are challenging problems. Distortion of the image due to an unequal rotation of the element or mirror at the catheter tip is a limitation of these systems. Advantages of the mechanical probes include high-resolution imaging and absence of near field artifact. The mechanically rotating devices produce an acceptable image but are unreliable and expensive.
Both stationary electronic systems and mechanical systems typically operate with acoustic frequencies from 10 to 30 MHz.
Medical interventions are often performed using endovascular techniques. These interventions include balloon dilatation, atherectomy, stent or device placement and removal, drug delivery, thrombolytic therapy, thrombectomy, vessel irradiation, embolic device delivery and thermal therapy by radio waves or microwaves. Guidance of these endovascular interventions is preferably accomplished using intravascular ultrasound imaging.
The present invention, using a solid-state actuator, is more reliable and less expensive than the rotating catheters with a single acoustic transducer. It can also easily have a central lumen for instrumentation or for a guidewire. In addition, the present invention produces a higher resolution image with fewer gaps in the information than the stationary imaging catheters. This invention creates a high-resolution ultrasound image with higher reliability and less expense than is currently available. This invention has the ability to generate real-time three-dimensional ultrasound images of the region surrounding the acoustic transducers.
Another significant advantage of the present invention is its ability to navigate tortuous vasculature in order to reach the site of the lesion in the body vessel or lumen. It is, because of its greater flexibility, useful in catheters used to treat lesions of the cerebrovasculature or distal coronary circulation. Interventional devices, delivering therapies such as atherectomy, thrombectomy and irradiation, stent placement or removal, thrombogenic therapy and thrombolytic therapy, guided by this high-resolution ultrasound system, offer improved guidance and precision of placement as well as flexibility at potentially reduced cost and higher reliability than that obtainable from rotating shaft devices. Thus, this invention fills a market demand for a high resolution, reliable and inexpensive imaging and therapeutic catheter.
The present invention is a catheter comprising an array of ultrasound transducers and actuators along with signal processing, display, and power subsystems. The actuators on the catheter cause the array to oscillate. This allows the array to produce more imaging points of the object to be viewed than a non-rotating or a stationary array. Additional computer processing of the ultrasound data produces an image with a higher resolution than images produced from data from a non-oscillating transducer array.
The present invention comprises a catheter, or axially elongate structure, which has a distal tip and a proximal end. The catheter optionally comprises a central lumen or a guidewire tip. The central lumen is often used for guidewire passage. It may also comprise additional lumens for purposes such as balloon inflation and deflation, stent deployment, device retrieval, contrast media or material injection, electromagnetic emissions and drug injection or removal. The distal tip comprises an array of at least one transducer for transmitting ultrasound energy radially outward, an array of at least one transducer for receiving ultrasound signals, and one or more actuators. The transmitting and receiving transducers may optionally be the same physical entity. The transmitting and receiving transducers are electrically connected to the proximal end of the catheter by a transmission line, cable or wire bundle, which is electrically connected to a decoder, a power generator, and a display instrument. The actuators are also electrically connected to the proximal end of the catheter with a transmission line, cable or wire bundle, which is electrically connected to a power supply. The ultrasound transducer array on the distal tip of the catheter transmits and receives ultrasound signals, which are processed by a computer to create an image of the object subjected to the ultrasound signals.
The transducer array, located near the distal tip of the catheter, rotates clockwise and then counterclockwise either with the rest of the catheter or, preferably independent of the catheter. The array may be rotated through an angle equal to or less than 360 degrees. Most advantageously, the array is rotated sufficiently to fill in the information gaps but not more than required to minimize the requirements of the actuator and linkages. The array is then capable of rotating backwards the same amount. The net motion is a rotating oscillation or a vibration. The oscillating array may be optionally covered with a non-oscillating shield. Preferentially, the array will be rotated much less than 360 degrees so multiple transducers are required in the array to maintain a full field of view.
In one embodiment, the distal tip of the catheter comprises an imaging array that is directed forward as well as the imaging array that is directed radially outward. The forward directed array allows for acquisition of additional information on the vessel distal to the catheter.
The present invention does not continually rotate. It vibrates rotationally in the same manner as an agitator to gather data to fill in the missing information between array elements. The rotating array allows for imaging of a two-dimensional xe2x80x9cslice of piexe2x80x9d- or wedge-shaped segment of the lumen and surrounding tissue. This two-dimensional imaging region is orthogonal to the axis of the array and generally orthogonal to the axis of the catheter. By circumferentially vibrating, the array is caused to move to fill in any gaps in information that exist between adjacent array elements. Lost information between array elements is the reason stationary array systems offer less resolution than rotating transducer systems.
Since the movement of the array occurs only near the tip of the catheter, the catheter can be made very flexible up to the point of the array and, thus, able to negotiate tortuous vasculature. Stiff drive cables used for rotational systems would not pass through tight curves and could not function distal to serpentine or highly tortuous vascular pathways. The actuators and array of the present invention can be made very small to accommodate high flexibility requirements of catheters needed to navigate tortuous vasculature and still function.
In one embodiment of the present invention, the transducer array is oscillated circumferentially, and in addition, rocked back and forth along the axis of the catheter to provide imaging information in three-dimensional space around at least a portion the tip. Actuators rotate the array circumferentially as well as axially, with respect to the axis of the catheter, to create a pyramidal-shaped imaging volume with a spherical exterior around each transducer of the array. The three-dimensional information is also obtainable in a spherical volume around the transducer array when it is designed with overlapping fields of view.
The preferred embodiment for vibrating or agitating the distal tip of the catheter is a nitinol actuator or sets of nitinol actuators mounted to cause movement of the transducer array. When the nitinol is exposed to electrical current, it changes dimensions due to resistive heating. When the electric current is removed, the nitinol returns to its original dimensions. Allowance for hysteresis must be made. By counter-attaching the actuators, they can be alternately activated and deactivated causing the transducer array to alternately vibrate clockwise and then counterclockwise or to pivot forward and backward axially. This type of actuator may be used for back and forth motion of the array along the axis of the catheter as well as circumferential motion. The actuator set may be built with separate actuators or as a single system capable of moving the array through two-dimensions to create the three-dimensional image. Counter-attached actuators could also be replaced with a single actuator using a spring return or other mechanism to ensure correct reverse motion when the power is turned off to the single actuator.
In another embodiment, the invention includes apparatus for cutting or excising atheroma, thrombus or other tissue from the interior of the body vessel or lumen. This apparatus comprises an actuator, which may or may not be the same as that which drives the imaging array, and cutting elements that act to cut tissue. The cutting elements may be disposed within a window on the side of the catheter to perform directional atherectomy or thrombectomy. The cutting elements may also be disposed in the forward direction to allow for channeling when the catheter is advanced. The invention also comprises catheter lumen structures and systems to provide suction to assist in the removal of the excised material.
In yet another embodiment, the invention comprises apparatus for illuminating the body vessel or lumen with electromagnetic radiation at wavelengths from gamma rays to radio waves. Visible light delivery may be accomplished using fiber-optic channels to transmit light in the visible, infrared or ultraviolet range. Ionizing radiation may be generated from a radioactive source, such as Iridium 192, Iodine 131, Iodine 125, Palladium 109, Strontium 90, Cobalt 57 and Cobalt 60, mounted to the tip of the catheter. Examples of ionizing radiation are electrons, positrons, beta particles, gamma rays and X-rays. A removable shield may be provided to allow irradiation only at the desired site. A microwave, X-ray or radio frequency (RF) wave source may also be mounted to the tip of the catheter. Power for the X-ray source, microwave or RF transducer is carried through the catheter by an electrical cable, wires or group of wires.
In another embodiment, the invention comprises a catheter capable of deploying or retrieving a device such as a stent, balloon dilator or vaso-occlusive material while monitoring the deployment or its result with the imaging array. In this embodiment, the array might be internal to the catheter or external to the catheter. The catheter may be placed through the lumen of one or more guiding catheters to facilitate maneuvering of the catheter tip through the vasculature or other body lumen.
The two-dimensional image is processed and displayed, preferentially in real time, on a two-dimensional monitor. The three-dimensional image is processed using standard techniques and displayed, preferentially in real time, by mapping the image to a two-dimensional monitor. Three-dimensional systems such as holographic projectors may allow for full three-dimensional modeling. The key to processing of the image is coordination of instant array element position with its one-dimensional ultrasound mapping information. Moving the transducer in one dimension makes a two-dimensional image and moving the transducer in two dimensions results in three-dimensional information.